The Dutch called it the Spanish disease. The Russians called it the Polish disease. The French blamed the Italians and the Italians blamed the French.

Ever since Europe recorded the first epidemic of syphilis in 1495, fierce debate has raged over the origins of the best-known venereal disease. Was it a homegrown, Old World bug that suddenly stalked the boudoirs of Renaissance Europe? Or did Christopher Columbus bring the sexually transmitted infection back from the New World, just like tobacco?

The mystery has inspired poems, historical papers, scientific studies, books and, quite likely, barroom brawls through the centuries. But medical experts from Canada and the U.S. believe they have now solved it.

In an epic tale of detective work and serendipity, researchers say they have genetic evidence that Columbus and his men, after mingling with natives of the Americas, did indeed sail home to Europe with a secret stowaway - a bacterial strain that spawned one of human history's deadliest plagues.

"I definitely think that syphilis, or the progenitor strain that led to syphilis, came from the New World to the Old World. ... We found the closest relative of [the syphilis bacteria]in South America," said Kristin Harper, a researcher with Emory University in Atlanta and lead author of the report published online today in PLoS, the Public Library of Science journal.

The researchers tout their work as the most extensive genetic study ever undertaken of
Treponema, the bacterial species behind syphilis, and determined the sexually transmitted germ to be a mutated version of a microbe that originally came from the Western hemisphere.

Collected by a team of Canadian doctors who happened to be tending Guyana's poor, the crucial sample was scraped from the sores of children in a remote corner of the Amazon.

Co-author Michael Silverman, an infectious diseases specialist and assistant professor of medicine at the University of Toronto, said the children are Akwio, relatives of the native people Columbus encountered on his famed voyages to the New World.

"Europeans gave them guns, smallpox, tuberculosis and so many other illnesses," Dr. Silverman said, "so in a way it's nice to know something went the other way."

Both Ms. Harper and Dr. Silverman - who became unlikely partners working an age-old puzzle - believe syphilis to be a tragic story of a New World bug transformed by sexual contact with Old World men.

European plague

Before antibiotics made syphilis a highly curable infection, it killed five million after it emerged in 15th-century Europe, some estimates say.

Ulcers and weeping sores spread from the genitals to cover the entire body. It could scar bones and dement the brain, casting the sheen of madness over its victims.

Ms. Harper was captivated by the syphilis mystery after reading a book about it as a 21-year-old college student. "It was the most amazing thing. I was totally fascinated. I knew I was going to try and answer that question."

She read that the plague first broke out among French troops invading Naples in 1494 and that Columbus and his men, just returned from the Americas, were immediately suspect; there were reports of syphilis symptoms among Columbus's crew. But others felt it had always been there, and only after 1495 did Europeans distinguish syphilis from other diseases such as leprosy.

In 2002, working toward her doctorate at Emory, Ms. Harper decided genetics might hold the answer. Scientists had just sequenced the full genome of
T. pallidum, the syphilis-causing bacteria, in 1998, and Ms. Harper thought if she could compare its DNA to related strains, she might be able to pinpoint its ancestor.

Dr. Silverman never intended to work in South America. He had just graduated as an infectious disease specialist and was eager to start a practice, but an older physician who had spent a lifetime caring for patients in impoverished regions convinced him to fly to Guyana in 1993.

That trip launched an annual expedition, and in 1996 Dr. Silverman helped found Ve'ahavta, a Canadian Jewish Humanitarian and Relief Committee. As its medical director, he now leads professional volunteers to Guyana each winter.